The present application is directed to a new class of carbon materials and their synthesis.
The conventional carbon materials are graphite, graphitelike ceramics or diamond and diamond-like ceramics. These materials are produced from carbon-containing compounds; oil, gases, coal, wood, coke, soot, graphite powder, diamond powder, hydrocarbons, polymers or mined as natural minerals. The lattice of graphite consist of planar layers of hexagons, where the carbon atoms have sp2-hybridization of the electron shells. The lattice of diamond consists of tetragons, where the carbon atoms have sp3-hybridization of the electron shells. Graphite is a very soft and weak material, with a hardness of 1 on the Mohs scale (1-2 for some graphite-like ceramics), it is conductive, sometimes referred to as a semimetal. Diamond is an extremely hard and tough material with a Mohs hardness of 10, it is non-conductive, but may be made semiconductive with doping.
Recently, much study has been made of ordered carbon molecules having distinct geometries, such as spheres (known as xe2x80x9cbuckyballsxe2x80x9d) and tubular shapes (xe2x80x9cnanotubesxe2x80x9d), these geometric shapes are generally comprised of relatively large numbers of carbon atoms such as C60, C70, C80 etc. These ordered carbon molecules are often referred to as xe2x80x9cFullerenesxe2x80x9d after the architect Buckminster Fuller, whose geometric designs the molecules resemble. The new carbon materials are synthesized (sintered) using powder metallurgy and/or ceramic pressing techniques from relatively pure amounts of ordered carbon nanoparticles such as C60 buckyballs (which have a spherical icosahedral symmetry) and nanotubes (which can be thought of as a tubular micro-crystal of graphite or a much elongated buckyball with open or closed ends) at high pressures and high temperatures (HPHT).
The new carbon materials are formed by pressing and heating of powder in the form of specially prepared fullerenes. These carbon materials are much harder than graphite and graphite like ceramics and are almost as hard as diamond, depending on the starting fullerenes, the pressing and heating parameters. These new carbon materials are conductive like graphite. The material can be formed by powder metallurgy techniques into any shape (cylinders, balls, tubes, rods, cones, foils, fibers or others). The pressure of compacting is from 1.0-10.0 GPa, the temperature is 300-1000xc2x0 C. and the period of time is from 1-10000 second. The special carbon soots are: (a) nanotube like, (b) buckyball like, or (C) mixtures of the same with similar diameters (one dimension size) of particles of 0.7-7.0 nm. The particles are pure carbon of 99% or more preferably 99.9+ % (or specially doped by other elements), separated by a narrow range of diameters, for example 0.7-1.0 nm;
The physical properties of the new carbon materials that are produced depend on the type and purity of the starting fullerenes. A strong carbon conductive material is formed by HPHT processing when the starting fullerenes comprise purified single wall nanotubes (or a mixture of single walled nanotubes and buckyballs) which has a hardness (7-9xc2xd on the Mohs Scale) greater than that of steel but less than that of silicon carbide (SiC). When the starting fullerenes comprise purified C60 buckyballs of uniform size an extremely hard (9xc2xd-10 on the Mohs Scale) conductive amorphous carbon material is formed under HPHT processing which has a hardness greater than that of silicon carbide and which is only slightly less hard than non-conductive diamond or cubic boron nitride. The new carbon materials may be formed within porous ceramic composite xe2x80x9cspongesxe2x80x9d to form other useful engineering materials by first impregnating the porous ceramic with the appropriate carbon compound and then converting them directly into the new carbon materials.
In particular, the two new carbon materials; 1) nanotube based sintered carbon material and 2) buckyball based sintered carbon material, exhibit hardnesses better than stainless steel (for nanotube based sintered carbon material) and near that of diamond (for buckyball based sintered carbon material). These materials are near isotropic xe2x80x9cpolymericxe2x80x9d materials, not poly or single crystalline materials. The polymeric isotropicity is what sets these materials apartxe2x80x94they are extremely tough, greatly resisting fracturing in comparison to c-BN or diamond or other crystals.
Synthesis of the new carbon materials has been demonstrated for millimeter sized pellets, which allow characterization of mechanical, electrical and other properties that are pertinent to military, industrial and scientific applications. The new carbon materials, with their high strength and toughness, may well fulfill the need for lightweight engineering materials for military, aerospace, automotive, and other industries. Since the materials are conductive, they may also be superconductive or be made semiconductive, in either case especially with proper dopants. It is theorized that the new carbon material is a semimetal and that the new carbon material based ceramics may have the metallic and semiconductive type of conductivity depending on dopants and parameters of synthesis.
Traditional graphite may be transformed into diamond at pressure of 15 GPa and temperature of 4000xc2x0 C. Graphite mixed with metals Ni, Fe, Co or alloys or hydrocarbons may be transformed into diamond in the P,T-region of the thermodynamical stability of diamond, for example at pressure of 5.5 GPa and temperature of 1500xc2x0 C. Graphite may be transformed into diamond in presence of atomic hydrogen and a diamond substrate in the P,T region of the thermodynamical stability of graphite, for example at low pressure of 0.104 Mpa and a graphite substrate temperature of 2000xc2x0 C. (if the temperature of the diamond substrate is 600-1000xc2x0 C). Conversely, diamond may be transformed into graphite at pressure of 0.1 Mpa and temperature of 2000xc2x0 C. Diamond mixed with metals Ni, Fe, Co or alloys may be transformed into graphite in P,T-region of the thermodynamical stability of graphite, for example at pressure of 0.1 Mpa and temperature of 1000xc2x0 C. in inert gas.
It has also been found that the buckyball based sintered carbon material can be transformed into polycrystalline or monocrystalline diamond at temperatures and pressures less that than needed for graphite. Furthermore, the buckyball based sintered carbon material may be transformed into monocrystalline diamond in the presence of alloys that do not catalyze the transformation of graphite into diamond.
The new buckyball based sintered carbon material can be used to provide ceramic composite materials. It was found that the smallest particles of carbon soot (buckyball C60) have the property of superplasticity in the temperature range of 200-400xc2x0 C. at pressures of 0.01 to at least 1.0 GPa. Graphite, diamond, B4C, WC/Co, Cu, Ti, TiC, SiC, Be, W, B, Fe and other porous sponges were prepared by various standard methods and impregnated with carbon soot at a pressure of 1.0 GPa and a temperature of 300xc2x0 C. The sample then was cooled, the pressure was thereafter increased to 2.5 GPa and the temperature increased to 400xc2x0 C. and held for 1000 sec. The particles of soot were sintered together inside the pores by HPHT treatment to produce composites with a new carbon material matrix which was found to be harder than silicon carbide (30 Gpa).